Four strains of aerobic heterotrophic bacteria were isolated on crude oil with the aim to test whether their presence and activity might support the growth of cyanobacteria in oil-polluted microbial mats and whether the cyanobacterial exudates might play a role in stimulating their degradative activities. The strains were phylogenetically related to known oil-degrading species from the genera Marinobacter, Pseudomonas and Sphingomonas. Three strains (GM41, GM61 and GM63) grew well on C5-C18 alkanes but not on 7 tested aromatics, whereas one strain (i.e. GM42) grew best on phenanthrene and pentane. All strains showed ability to metabolize a range of cyanobacterial photosynthetic and fermentative exudates. In coculture experiments, the addition of the Pseudomonas-related GM41 strain to the cyanobacterium Synechocystis PCC6803, found in the same mat, resulted in 8-fold increase in the cyanobacterial biomass. This growth was more pronounced when hexadecane was added to the culture medium. The addition of representative substrates of cyanobacterial exudates to the phenanthrene-degrading strain GM42 resulted in variable effects. While acetate, pyruvate and glucose enhanced phenanthrene degradation, alanine and butanol showed no effect. We conclude that aerobic heterotrophic bacteria-cyanobacteria consortia can be very useful for bioremediating oil-polluted sites, circumventing the costly use of organic and inorganic fertilizers.
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